Field of the Invention
Embodiments of the invention relate to synthesis and use of porous silicon materials.
Background of the Related Art
As a typical kind of porous semiconducting material, porous silicon materials have been long studied due to their special chemical and physical properties and wide applications in different areas. For example, porous silicon materials are deeply investigated in optoelectronic and censoring due to their light-emitting properties. Porous silicon materials are also used in drug and gene delivery research because of their high porosity and bio-compatibility. In addition, potential applications of porous silicon materials in food fortification are being explored.
In addition to its attractiveness for use in the above applications, porous silicon has gained popularity in the field of lithium-ion (“Li-ion”) batteries. This is due to the use of silicon-based anode materials. The porous structure is considered as an effective way to compensate for the huge volume change (about 300%) of the silicon anode during the electrochemical process. This tends to provide better performance than non-porous anode materials.
There are two well-established techniques to produce porous silicon materials. These are anodization and stain etching, specifically. Unfortunately, both methods require a solid crystallized silicon precursor. This results in a corresponding low porosity yield. In addition, both methods need large volumes of hydrofluoric acid (“HF”), which is difficult to safely handle and is not environmentally friendly. Both disadvantages made these two methods high-cost and low-efficiency.
Some alternative preparations that avoid using a solid silicon precursor were reported in recent years. These include chemical reduction of porous silicon, and thermal annealing followed by hydrofluoric acid etching with templates. Pre-formed porous precursor or pore templates are still necessary in the process to obtain the pores. Unfortunately hydrofluoric acid, with its many disadvantages, is still required.